Our overall objective is to better understand how information is transferred and processed within cerebellar cortical circuitry. The proposed experiments address issues raised by recent experimental results which suggest that a re-examination of previously held views about information transfer from cerebellar granule cells to cerebellar Purkinje cells is necessary. Based on these recent studies, we have proposed, for example, that a single granule cell layer activation may have two distinctly different influences on overlying and nearby Purkinje cells. This and other related issues regarding this cerebellar circuitry will be addressed in four sets of experiments with the following specific aims: 1) to study the synaptic effects of granule cell-parallel fiber activity on Purkinje cells at varying distances from the focus of granule cell layer activation; 2) to study the synaptic effects on Purkinje cells of the convergence of activity evoked in different granule cell layer loci: 3) to study the amplitudes and temporal delays of parallel fiber synaptic effects on intracortical inhibitory interneurons; and 4) to study interactions between Purkinje cells via recurrent collaterals directly by recording intracellularly from two cells simultaneously. These experiments will employ intracellular anatomical and physiological techniques using laboratory rats as subjects. Together, these studies will help fill conspicuous gaps in knowledge regarding the fundamental organizational principles underlying the neural processing of information in cerebellar cortex.